Formal:
* Therefore
* Thus
* Consequently
* Hence
* As a result
* Accordingly
* In light of this
* Due to this
* Because of this
* For this cause
Informal:
* So
* That's why
* That's the reason
* Because of that
* On account of that
* This is why
* For that reason
* And that's why
More specific:
* To address this
* In response to this
* To remedy this
* In light of these circumstances
The best alternative will depend on the specific context and the tone you want to convey.